This invention relates to an improved signal generator for an internal combustion engine. More particularly, it relates to a signal generator of the type which is disposed inside a distributor together with an ignition coil.
An internal combustion engine is commonly equipped with a signal generator which generates electrical signals in synchrony with the rotation of the engine. The electrical signals are usually in the form of pulses having a rising edge and a falling edge which correspond to prescribed crankshaft angles of the engine, and thus to prescribed positions with respect to top dead center of the piston of each cylinder of the engine. These signals are input to an engine controller. Based on the timing of the signals, the controller controls the ignition timing, the fuel injection, and other aspects of engine operation which must be performed with a precise timing.
One conventional type of signal generator is disposed inside a distributor housing and detects the rotation of the distributor shaft. In this type of signal generator, a Hall-effect sensor and a magnet are disposed inside the distributor housing with a gap between the Hall-effect sensor and the magnet. The Hall-effect sensor includes a Hall element which generates an analog voltage corresponding to the strength of the magnetic field acting on it. The distributor shaft has a plurality of metallic vanes attached to it which rotate together with the distributor shaft. As the vanes rotate, they pass through the gap between the Hall-effect sensor and the magnet and change the flux which acts on the Hall element. As a result, the output voltage of the Hall element momentarily changes each time one of the vanes passes through the gap. The Hall-effect sensor generates a digital signal in the form of pulses corresponding to the changes in the output voltage of the Hall element. The distributor shaft is rotated in synchrony with the engine, so by appropriately choosing the number and the width of the vanes, the rising and falling edges of the output pulses of the Hall-effect sensor can be made to occur at prescribed rotational angles of the crankshaft of the engine and can be used for controlling the engine timing.
In some new automobiles, the ignition coil for the engine is disposed inside the distributor housing together with the signal generator. When current flows through the ignition coil, a magnetic field is generated which combines with the magnetic field generated by the magnet of the signal generator. In a conventional arrangement, the magnetic field generated by the ignition coil combines additively with the magnetic field generated by the magnet of the signal generator. The combined magnetic fields affect the output voltage of the Hall element in a manner such that the changes in the output voltage of the Hall element as the vanes rotate can not be detected. As a result, the Hall-effect sensor does not generate output pulses at the proper intervals, and the engine timing can not be properly controlled.